Question: Which of these numbers is composite? ${23,\ 47,\ 53,\ 65,\ 73}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 23, 47, 53, and 73 each have only two factors. The factors of 65 are 1, 5, 13, and 65. Thus, 65 is the composite number.